It has already been proposed to take permanent measurements in the tread of a tire while a vehicle equipped therewith is moving, in order to know in real time the stresses which develop between a tire and the ground. German Offenlegungsschrift DE 39 37 966 A1 may be consulted on this subject. Although of interest, such information is still insufficient, since the driver or even an automatic device, such as those covered by well known designations in the automotive field, e.g., “ABS” or “ESP”, is still incapable of anticipating a deterioration in the adherence. One therefore makes do with noting a posteriori the exceeding of an adherence limit, and as rapid action as possible is taken to control the vehicle.
There exists in this respect a requirement to obtain indications “in real time” of the adherence conditions capable of affecting, in the moments which follow, the behavior of a vehicle, notably in cases where it undergoes a substantial acceleration, due to motive or braking forces or to a change in path. The present invention is aimed at supplying means and methods of providing such “real time” indications in an effective manner, by procuring as realistic information as possible on the safety margin which subsists in the driving of the vehicle.
As used herein, the following terms have the meanings set forth below:                “measuring element” means a part of the tread of the tire, e.g., a tread block or rib, whose structure is adapted to the aim pursued by the invention;        
“adherence potential” means the ratio between the overall maximum tangential force which a measuring element, considered in its totality, may undergo during its contact with the ground at a given place, and the normal force applied to that element;                “friction potential” means the ratio between the local tangential stress and the local vertical stress which are exerted at a given point onto a rubber element sliding over the ground; and        “available adherence margin” is the difference between the adherence potential of an element and the ratio between the overall tangential force and the overall vertical force actually applied to that element, considered in its totality, during its passage in the contact area.        